1. Field of the Invention
The present invention generally relates to a container, and more particularly to such containers that are typically made of polyester and are capable of being filled with hot liquid. It also relates to an improved dome construction for such containers.
2. Statement of Related Art
xe2x80x9cHot-fillxe2x80x9d applications impose significant and complex mechanical stress on the structure of a plastic container due to thermal stress, hydraulic pressure upon filling and immediately after capping the container, and vacuum pressure as the fluid cools.
Thermal stress is applied to the walls of the container upon introduction of hot fluid. The hot fluid causes the container walls to first soften and then shrink unevenly, causing distortion of the container. The plastic material (e.g., polyester) is often, therefore, heat-treated to induce molecular changes resulting in a container that exhibits thermal stability.
Pressure and stress also act upon the sidewalls of a heat resistant container during the filling process and for a significant period of time thereafter. When the container is filled with hot fluid and sealed, the container is subjected to an increased internal pressure. As the liquid and the air headspace under the cap subsequently cools, thermal contraction results in a decrease in pressure in the container. The vacuum created by this cooling tends to mechanically deform the container walls.
Containers for liquid are often shipped in cardboard boxes that are stacked on top of each other during storage and shipping. The containers have exhibited a limited ability to withstand top loading during filling, capping and stacking for transportation. Overcoming these problems is important because it would decrease the likelihood of a container""s top or shoulder being crushed, as well as inhibiting ovalization in this area. It is important to be able to stack containers so as to maximize the use of shipping space. Due to the weight of liquid-filled containers, the boxes often need reinforcing such as egg crate dividers to prevent crushing of the containers. The vulnerability of the containers to crushing can be increased by the deformation resulting from the above-mentioned vacuum.
A particular problem which can result from the hot-filling procedure is a decrease in the container""s ability to withstand top loading during filling, capping and labeling. Because of the decreased container rigidity immediately after filling and after cooling, even heat set containers are less able to resist loads imparted through the top or upper portion of the container, such as when the containers are stacked one upon the other for storage and shipping. Similar top loads are imparted to the container when it is dropped and lands on the upper portion or mouth of the container. As a result of this top loading, the container can become deformed and undesirable to the consumer.
Embodiments of the invention provide a container dome structure that helps reduce the container deformation described above. In addition, the invention provides a container dome structure with sufficient topload strength to allow significant reduction in secondary packaging requirements. For example, the need for using xe2x80x9cegg crate dividersxe2x80x9d may be reduced or eliminated.
Particular embodiments of the invention provide a blow molded container having a base, a body portion attached to the base, a concave waist attached to the body portion, a dome attached to the waist, a plurality of structural ribs, and a finish attached to the dome. The finish has an opening and a portion of the dome is located between the panels and the waist. The dome has a plurality of panels arranged around a perimeter of the dome. Each of the structural ribs is located between two adjacent panels and is raised relative to the panels.
Other embodiments of the invention provide a blow molded container having a base, a body portion attached to the base, a concave waist attached to the body portion, a dome attached to the waist, four structural ribs, and a finish attached to the dome. The finish has an opening. The dome has four panels evenly spaced around a perimeter of the dome. Each of the structural ribs is located between two adjacent panels. A portion of the dome is located between the panels and the waist, is circular in cross section, and has a larger diameter than the waist. Each of the structural ribs is raised relative to the panels and at least one of the structural ribs is incorporated into a graphical image that represents a material for which the container is made.